The Bella centre is the focal point for climate activists who are aiming to invade the summit today. Around the city, some 150 arrests have been made this morning as part of an intensification of security to keep the lid on actions in the conference centre as the first of 115 world leaders arrives in Copenhagen amid the major protests.

In a separate development, hundreds of non-government groups are to be individually banned from the centre or have their numbers slashed from tomorrow to make way for world leaders. Only 1,000 people from civil society will be allowed in to the conference hall tomorrow, and 90 on Friday.

This has provoked dismay with many delegates seeing it as a deliberate attempt to muzzle public voices and criticism of world leaders.

Andy Atkins, the director of Friends of the Earth UK, said: "We understand there has been unhappiness at some of the actions inside, but no formal explanation has been given. It is completely out of order. People are outraged at what is going on. Big mainstream organisations are being muzzled. This is madness."

Around 50 members of the group staged a sit-in at the inner lobby of the Bella centre. Friends of the Earth international is the largest international environmental federation in the world with groups in more than 70 countries.

TckTckTck is a global alliance of environment, development, church and human rights groups, Avaaz is a web-based pressure group which has organised thousands of climate meetings around the world. Together they claim to represent more than 10 million people.

"So many people are being excluded. The process is farcical. Civil society is being shut up, developing countries are being shut up, critical voices are being shut up," said Nicola Bullard, working with Focus on The Global South, a member of the climate justice movement.

"There's a lot of frustration among civil society that we are not moving quickly enough. There are obstructionist tactics. There are debates and arguments. As civil society we feel that they don't care," said Tom Goldtooth, a Bolivian with the Indigeous Environmental Network. "We feel they are negotiating for the sake of corporations instead of for the betterment of the people of the world."

In a later development, the UN offered Friends of the Earth International 12 places for the conference, but this was declined.

Magda Stoczkiewicz, director of Friends of the Earth Europe, said: "If Friends of the Earth is not allowed inside the UN negotiations we cannot play our crucial role in bringing the voices of citizens to the talks, especially the voices of those who are disadvantaged and already suffering most because of climate change. These draconian measures are completely unjustified. We said no to accepting 12 places."